The delayed coker process converts the residue from heavy, high sulfur crudes into transportation fuels. The kerosene stream from the coker process is known as coker kerosene. It comprises hydrocarbons in the range of C9 to C20 and has a boiling point in the range of about 140° C. to about 320° C. It has a T5 point of 150° C. and a T95 point of 295° C. measured according to ASTM D86.
Coker kerosene contains high levels of sulfur (e.g., about 2 to about 5 wt %) and nitrogen (e.g., about 600-1000 wppm). Coker kerosene has to be hydrotreated to reduce the levels of sulfur and nitrogen before it can be treated in a separation unit, such as Molex™ to separate the n-paraffins from the non-normal hydrocarbons. The feed specifications for the Molex™ process include a sulfur level of less than 1 wppm, and a maximum nitrogen level of 0.5 wppm. Kerosene also contains olefins, and the olefins are saturated during the hydrotreating process. Another feed specification for the Molex™ process is a bromine index (BI) in the range of less than about 150.
In order to meet the sulfur, nitrogen, and BI specifications for a coker kerosene feed, severe hydrotreating at pressure in the range of about 7.6 MPa(g) (1100 psig) to about 8.3 MPa(g) (1200 psig) is required.
However, it is preferable to hydrotreat at the lowest possible pressure to reduce the capital cost of the unit. The sulfur and nitrogen specifications can be met at lower pressures, e.g., in the range of about 4.8 MPa(g) (700 psig) to about 6.2 MPa(g) (900 psig). However, the BI specification cannot be met by hydrotreating at that pressure.
Normally, a post treat reactor loaded with a hydrotreating catalyst is installed downstream of the main hydrotreating reactor to obtain the required BI. The post treat reactor has to operate at sufficiently high pressure and catalyst volume to meet the BI. Due to equilibrium limitations, the temperature of the post treat reactor needs to be in the range of about 250° C. and 350° C. to ensure that the required olefin saturation is obtained to meet BI requirement.
Even with the post treat reactor, it is not always possible to obtain BI values in the range of 50-100.
There is a need for lower cost processes to upgrade coker kerosene.